Various kinds of measures have been conventionally taken in order to prevent a smudge on a surface of an article. The body of an automobile, for example, is easily smudged with dusts and combustion products such as an exhaust gas. For this reason, a measure has been widely adopted that wax is applied on a surface of the body to thereby prevent adhesion of a smudge. This is because the body surface is rendered water repellent by forming a wax film thereon, whereby when water is brought into contact with the body surface, it is divided into water droplets, which roll down the body surface, so that it is prevented that a smudge component in droplets adheres and stays on the body surface and in addition, even if the smudge component has adhered to the body surface, the adhered smudge is easily removed away by washing with water.
Further, products connected to a plumbing system, such as a bathtub, a kitchen sink, a bathroom sink and the like, when being used, are brought into contact with various kinds of substances or agents such as a soapy water, a facial cleansing agent, a hair dye and the like containing oil and an oily component as well as water. Smudges on such products connecting to a plumbing system are thought to occur by adhesion of the oily materials, soap scum which is a calcium salt of a soap, or the like to surfaces of the products, alone or together with dusts. In order to prevent smudges of the products, a water repellency treatment has also conventionally applied on a glazed surface which is formed on surfaces of the products and is of a glassy nature with, for example, a wax, a fluorine containing material or the like, so that smudges do not remain on the glazed surface. Prevention of smudge adhesion on a surface of interior and exterior finish of a house, a toilet bowl, a sign board, a sign, stone material such as a gravestone, a metal and the like has been tried.
On the other hand, it has been known for a long time to apply a surfactant on a surface of a base material to modify the surface to a hydrophilic nature, and it is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 52-101680 and the like that a water-soluble organic polymer such as polyacrylic acid or polyvinyl alcohol is added into and mixed with a surfactant to thereby improve maintainability of hydrophilicity. Furthermore, by Japanese Examined Patent Application (JP-B) No. 5-67330 and the like, a method has been known in which hydrophilic materials such as celluloses, glycols and glycerin are fixedly applied onto an outer surface and into an inner part of a porous film made of a hydrophobic polymer through a film made of a copolymer of polyvinyl alcohol and vinyl acetate.
However, in a conventional water repellency treatment with a wax or the like, the water repellency effect was unable to be said sufficient, or even if a sufficient water repellency treatment was applied at the first stage, the effect disappeared shortly later; therefore, it was unable to be said that an anti-fouling effect was exhibited at a sufficient level over a long term.
On the other hand, as to hydrophilic coating, a conventional hydrophilic coating was effective only temporarily or for a short time in imparting hydrophilicity and not only was a sufficient durability of a water repellency effect hard to be expected, but also a water film was difficult to be uniform and a transmission image and a reflection image were distorted, having led to a problem of hard applicability to the above described products and the like.
In addition, various measures such as a fluorine treatment have also been studied on prevention of a smudge of false teeth and generation of a smell thereof, whereas the current state of the art is not at a level that a sufficient effect is kept active over a long term once a treatment is applied.
As a result of a study on and investigation into such a problem in order to solve it, the inventor previously invented an anti-fouling coating solution containing an inorganic polysilazane, a diluting solvent and a catalyst, capable of forming a silica coating at room temperature and filed an application for a patent (Japanese Patent Application No. 2001-131494). In this application, the anti-fouling coating solution is applied on a base material and thereafter left at ordinary temperature to thereby convert inorganic polysilazane to silica by the action of a catalyst and to form a rigid and dense film excellent in adhesion with the base material on a surface of the base material. The silica coating formed by conversion of the inorganic polysilazane can impart a hydrophilic effect and an anti-fouling effect maintained over a long term to the base material. Hence, the anti-fouling coating solution having been proposed by the inventor can form a hydrophilic film having an excellent anti-fouling function on bodies of an automobile, a tramcar, an airplane and the like, wheels of an automobile, interior and exterior finish of a house, products connected to a plumbing system and used at a place where water is used such as a toilet bowl, a kitchen sink, a bathroom sink and a bathtub, a sign board, a sign, a plastic product, a glass product, a stone material, false teeth and the like; and impart a preferable ant-fouling characteristic maintained over a long term to surfaces of the above things with ease.
In order to convert the anti-fouling coating solution perfectly to a hydrophilic and dense silica coating as described above, however, it usually takes a time of the order of one month after coating in a condition of being left at ordinary temperature. For this reason, in a case where the anti-fouling coating solution is applied onto the body of an automobile, for example, it is thought that, if it is new, it could be used by a final user before the anti-fouling coating solution is converted sufficiently to a silica coating after the anti-fouling solution is applied to the car in a factory and the car is delivered to the final user, and in the case, a smudge adheres to the body because of use in an immature state. It is also thought that, after an anti-fouling coating solution is applied on a car having already owned by a user in order to form an anti-fouling coat, the car is used before a not long time elapses after the coating, thereby adhering a smudge thereto. That is, the anti-fouling coating solution was unable to impart an intrinsic hydrophilic and dense coating to an article in some case according to a use mode of the article, in such case no anti-fouling effect was able to be exhibited.
The inventor, as a result of an eager study, has found that in the case where a coating solution containing polysilazane, including the above-described anti-fouling coating solution, is applied onto a base material, and thereafter, polysilazane in the coating film formed is converted to silica to form a hydrophilic and dense silica coating excellent in anti-fouling property on the surface of the base material, by application of an aqueous solution containing a specific surfactant on a coating film formed by applying a polysilazane-containing coating solution and drying, hydrophilicity of the coating film is promoted to an extremely high level and the coating film shows sufficient hydrophilicity after about 10 min. of the application, thereby being able to prevent adhesion of a smudge.
The polysilazane-containing coating film, as described above, completes conversion to silica over about one month after application in an ordinary case, and over about one month after application in a case where a hydrophilicity promoting solution of the invention is applied as well. However, there are cases where smudges adhere on the coating during the about one month or where even after the coating film is converted to silica, smudges adhere during the use over a long term. Such smudges link to reduction in hydrophilicity of the coating film, which degrades an anti-fouling effect of the coating solution. The inventor has found that smudges are wiped off with a solution obtained by further diluting a hydrophilicity promoting agent with water, thereby enabling removal of them without degrading hydrophilicity of the anti-fouling film. A hydrophilicity maintaining agent of the invention has been made based on the findings described above.